Page 244 - Materials Chemistry, Second Edition

L1644_C06.fm Page 217 Monday, October 20, 2003 12:06 PM

6.4 MATHEMATICAL FOUNDATION

Because LCA and ERA belong to the environmental system analysis and are based
on models of the real world, it is evident that the first step is to base the general
strategy described so far on a mathematical framework that enables carrying out
further steps. It includes, in particular, a procedure that allows knowing the quantity,
situation and moment of the generation of the specific environmental interventions
in the LCI. As introduced in Chapter 2, Castells et al. (1995) have presented an
algorithm that uses an eco-vector. The different types of environmental loads, like
chemical substances, can be classified in categories according to their environmental
impacts; then different impact potentials can be calculated by the characterization
factors presented in Heijungs et al. (1992). For example, CO , CH , CFC-11 and
2
4
others can be aggregated in the global warming potential (GWP) and be expressed
as CO equivalents. The different chemicals are characterized by a specific weighting
2
~
factor, i.e., the eco-vector e is converted into a weighted eco-vector e , as shown
v
v
i
in Expression 6.1, where ev is the specific [EL (environmental load)/kg] of the ELi,
~ i eq i i
ev is the specific weighted [EL /kg] of the EL , and l is the specific weighting
factor of the EL .
i
i
˜ e = ˜ e = e i l i (6.1)
v v v
According to the goal of the general strategy, the eco-vector algorithm must be
changed in order to make possible the assessment of the actual impacts caused by
a specific process in a particular environment. Considering the example of a process
chain with three processes, each process (PR) consumes raw material (RM) or an
intermediate product (IP) and generates emissions and/or waste (SO , PM , Cd,
10
2
etc.) per functional unit to obtain the functional unit, the product. When the LCI
analysis is applied to the three processes, an eco-vector with the environmental
interventions for all three processes is obtained, as illustrated in Figure 6.3. It is
evident that the following LCIA generates only potential impacts because all site-
specific information is lost when the LCIA is carried out.

IP IP
RM PR1 PR2 PR3 Product

• Classification
SO 2 SO 2 SO 2 SO 2 • Characterization
PM10 + PM10 + PM10 = PM10 • Weighting
Cd Cd Cd Cd

Process specific eco-vectors Life-cycle eco-vector

FIGURE 6.3 Life-cycle inventory analysis according to the eco-vector principle (IP = inter-
mediate product, PR = process, RM = raw material). (Reprinted from J. Hazardous Mater.,
©
77, Sonnemann, G.W. et al., pp. 91–106, 2000 with permission from Elsevier.)

© 2004 CRC Press LLC